you could also rip them in strips and then use a tongue and grove shaper bit to make them almost like laminate flooring that would require fewer or almost no exposed nails. this would require using thicker plywood also. and you can find different types of hardwood plywood such as cherry or oak that is used to build cabinets that is meant to be exposed and has a good grain structure and no knots.

great idea on this. it is a lot cheaper than buying pre-finished flooring

Nice, looks good. Though I haven't installed this type of floor, I have seen floors where they take the plywood and then cut them into strips/planks. You can take these 4'x8' sheets and cut them into 8" planks, (actually by cutting them into 7 7/8" widths you will get 6 per panel. Mix up your planks from different sheets and you will perhaps never notice the same grain. Then install it like hardwood floors (the layout I mean), caulking and topnailing (countersink and fill). The result will be so many times better than laying down whole panels. You can get straight cuts by using a straight edge to guide your skilsaw or use a table saw. For something like this I will cut 3 strips coming from one factory edge and then cut the next three off the other factory edge, so as to minimize any cut error from compounding. Again, I don't mean any disrespect, good job. But a little more effort and you would have had a job many many times better. You could still install real hardwood over the 5mm 8" planks. No problem.

First, be selective about the plywood selection, Select pieces that resemble each other so that disparities don't pop out like a sore thumb.

Balance the panel layout in the room. That is, panels against the wall on opposite sides should be the same size.

The large panels are not proportionate to the room size. I formed grooves in my plywood at 2 feet on centers, and along the edges. With the panels matching each other in pattern and the grooves in the panels, everything seemed to belong to the space, and the balance of sizes topped it off.

Another approach would be to install the panels non-parallel to the walls, and staggered.